5-1. Field of the Present Invention
The present invention relates to a tablet system with inductive loops controlled by multi-channel switches set and cord less-battery less pointer apparatus and its signal transmitting and receiving method, and more particularly, to a tablet system with inductive loops controlled by bi-polar multi-channel switches set and cord less-battery less pointer apparatus and its signal transmitting and receiving method.
5-2. Description of the Prior Art
Since a handwriting input apparatus can replace a mouse and allow users to input words and pictures by hand, more easily than a mouse, the field of improvement of a handwriting input apparatus has developed rapidly in recent years. The early handwriting input apparatus replaces a mouse with a pen. In order to increase the convenience of operation for the user, a cordless pointer apparatus, such as a pen, a mouse, a puck or a stylus with a digitizer tablet is usually used. The tip of the cordless pen or stylus corresponds with the left key of the mouse. Although conventional pen-input products have existed for several years, similar kinds of products generally focus on the application of a single function such as graphing, drawing or Chinese text key-in.
The conventional electromagnetic inductive system is equipped with a digitizer tablet and a mouse or pen-transducer/pointer apparatus. Generally speaking, there are two modes of presented the position the pointer apparatus located on the active area of the tablet: the relative mode and the absolute mode. The mechanical or optical type mouse apparatus generally functions in the relative mode, that is to say, when the mouse glides on the surface of the mouse pad, the computer system receives the cursor information from the mouse and it can only identify the relative movement in X and Y directions. A common technique is to implement a pair of mutually perpendicular altering signals in the mouse, these two signals corresponding to the longitudinal and transverse movement of the mouse. In contrast, the cursor apparatus of the tablet, such as cordless pointer apparatus, generally functions in the absolute mode. As far as the computer system is concerned, once the pointer apparatus is operated and moved to another place on the active area of the tablet, the signal changes in order to response the new absolute coordinates of the pointer apparatus. Nowadays, there have already been several methods for positioning the pointer apparatus on the active area of the tablet, and the electromagnetic field inductive technique is the technique that generally applies to the absolute mode. The early transducer/pointer apparatus were connected to the tablet with a set of wires, delivering the information of coordinates and switch/pressure status to the computer system with interface. Some cordless transducers/pointer apparatus in the prior art indicated the use of different functions by changing the frequency and/or phase, the functions included, pressing down the button, pressing the tip of the pointer apparatus on the active area, and other similar functions. However, without careful handling, the change in frequency and phase could easily cause misjudgment in the desired function of the pointer apparatus because of various external factors such as metallic objects, noise signals, exterior electromagnetic fields, etc. These problems become extraordinarily obvious when it comes to tablets of larger size. The conventional technique for improvement made to the tablet system, allows users to operate the pointer apparatus with tablet system in dual mode, and therefore the information regarding relative mode and absolute mode can both be provided under the user's control.
The current pointer/input product is usually an electromagnetic inductive system. The electromagnetic inductive system usually comprises an electromagnetic pointer apparatus and a tablet. The electromagnetic pointer apparatus has an oscillation circuit and a battery, providing energy for transmitting the relative electromagnetic signal. Take the electromagnetic pointer apparatus for example, when the tip of the pointer apparatus is pressed, the inductance of the inductor changes, therefore the oscillation frequency also changes. The higher the pressure received by the pointer apparatus, the greater the inductance changes, and the oscillation frequency, therefore the magnitude of the pressure exerted upon the pointer apparatus tip can be obtained through the changing degree of frequency. There are also two switch keys on the side of the cordless pointer apparatus, the on/off status changes the transmitting frequency and the connecting/disconnecting a specific capacitor in the oscillation circuits. When the user presses the switch key, it can be identified through detecting the variation of frequency.
The tablet also comprises elements such as a detective loop, an amplifier, and an ADC and so on. The central writing area of this conventional handwriting tablet is plaited by inductive loops, the layout is composed of double layers of a PCB and the inductive loops with two axial arranged in an array of equal distance. The major use of these inductive loops is to induce the electromagnetic signal transmitted by the electromagnetic pointer apparatus. When the electromagnetic pointer apparatus transmits the electromagnetic signal, these inductive loops will induce the electromagnetic signal and the microprocessor will receive the processed information of the pointer apparatus through a signal processing circuit. Generally speaking, the inductive loops of the conventional electromagnetic inductive apparatus and its layout design makes the inductive loops a grid net with the X and Y axis arranged in an array at equal distance in order to induce the signal emitted from the electromagnetic pointer apparatus and figure out its absolute coordinates. Since the intensity of the magnetic field is an inverse proportion to the square of distance, the farther the distance between the electromagnetic pointer apparatus that's transmitting the electromagnetic field and the inductive loops, the weaker is the signal induced by the inductive loops; in contrast, the nearer the distance between the electromagnetic pointer apparatus that's transmitting the electromagnetic field and the inductive loops, the stronger is the signal induced by the inductive loops. Therefore, as long as the microprocessor of the tablet can scan through all the inductive loops one by one in sequence, and analyze the strength of the signals induced by each inductive loop, the inductive loops in which dominates the range the electromagnetic pointer apparatus located can be identified. The coordinates of its position can be figured out. However, as far as a tablet of a larger size is concerned, the number of inductive loops arranged also increases, and therefore more loop switches are needed.
On the other hand, the development of current information products is aimed at a high-speed and high data rate process with multiple and excellent functions. But as the speed of processing and data rate increase, the phenomenon of electromagnetic interference will happened often. In some specific occasions of operating tablet system, there are usually other information products being used. Therefore the conventional tablet is easily interfered with by exterior electromagnetic fields and thus misjudgment is a result. As far as the tablet of a larger active area is demanded in commerce is concerned, the number of inductive loops needed increases, and therefore the number of loop switches will also increase greatly without a doubt. This limits the miniaturization of a PCB for a handwriting tablet and makes it difficult to design and produce a tablet with the small boundary. Therefore, an electromagnetic inductive system with a battery-less pointer apparatus and multi-inductive loop layout with a coordinate-locating procedure is disclosed by the present invention according to the above said purpose. The multi-inductive loop layout of the present invention comprises a multi-inductive loop group deployed according to an inductive loop deployment table. The inductive loop layout in the inductive loop deployment table comprises a plurality of physical inductive loops that are distributed along the X and Y axis of the two-dimensional orthogonal coordinates system and each physical inductive loop comprises a plurality of logical inductive loops. As far as each physical inductive loop that's distributed in the same direction is concerned, the logical inductive loops that are adjacent to the two sides of each logical inductive loop belong to a different physical inductive loop. Besides, the scanning procedure is to scan the physical inductive loops with the loop deployment table built-in microprocessor. First, each loop switch is switched on its physical inductive loop in sequence to transmit an electromagnetic signal. When the battery-less pointer apparatus is in the region of the multi-inductive loop layout, it induces the electromagnetic energy transmitted by the physical inductive loop. After the cord less-batter less pointer apparatus induces and stores the energy, the bi-direction loop switch of the physical inductive loop stops transmitting energy and starts to induce the energy transmitted by the battery-less pointer apparatus. On the other hand, the positioning procedure of the battery-less pointer apparatus of the electromagnetic inductive system includes, ┌Full Scan┘ and its ┌Partial Scan┘ procedure of X and Y direction in order to detect the first signal, possessing the highest voltage, the second signal, possessing the voltage second to the highest, and the third signal, possessing the third highest voltage orderly and figure out the accurate coordinates of the battery-less pointer apparatus through the calculation of the internal circuit processing and microprocessor of the electromagnetic inductive system.
Besides, there are also different methods for controlling signal transmitting and receiving circuit between digitizer tablet system and cord less-battery less pointer apparatus in prior art. One of the methods is “Position Detecting Apparatus” shown in FIG. 1, U.S. Pat. No. 4,878,553, two ends of loop coil of which being connected with two respective analog selecting switch for controlling respectively signal transmitting/receiving; and another two analog synchronous switches have to be used for connecting transmitting circuit and receiving circuit to make loop coil transmit and receive signal. Therefore, four analog selecting switches have to be connected and used each time signal is transmitted or received. Since each analog selecting switch has “ON” impedance, the impedance in series connecting increases as more analog selecting switches are used, and therefore too much power will be consumed on impedance in series connection while transmitting/receiving, thus weakens the signal transmitted/received, and even stops digitizer tablet system from operating since cord less-battery less pointer apparatus cannot complete storage of energy in certain cycle and cannot transmit enough electromagnetic energy. Moreover, when conventional analog switch is in on/off action, since it needs longer response time, signal transmitting/receiving will be delayed as analog switches in series connection increases, which restricts response time of digitizer tablet system and thus affects processing speed of digitizer tablet system of greater area; and, the circuit can only transmit signal in one way, which means there is only one direction for signal to flow in loop coil, therefore there is still room for improvement in application efficiency of transmitting power.
Furthermore, in order to eliminate the defect caused by using analog selecting switch in above-mentioned U.S. Patent, in U.S. Pat. No. 5,330,210, analog selecting switch is replaced by three-status elements having function of logical element, the purpose of which is, with high speed response and low impedance of switched-on logical element, increasing power efficiency of transmitting/receiving to reduce signal decline and increase response speed caused by too many analog selecting switches. However, three-status element can be on in only one direction, therefore different logical elements and different routes have to be used while transmitting/receiving, and thus complicates the circuit and causes more noise and higher cost.